Message "to download and install the addon (.....) for public sessions" while it is installed.

Look in the registry in this key if there is indeed a 1 on the front of packs BTB concerned:Windows 32 bitsHKEY_LOCAL_MACHINE\SOFTWARE\SCi Games\Richard Burns Rally\RSRBR\PacksBTBorWindows 64 bitsHKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\SCi Games\Richard Burns Rally\RSRBR\PacksBTB